This application claims the priority of German patent documents 197 26 409.3, filed Jun. 21, 1997; 197 26 410.7, filed Jun. 21, 1997; and PCT Application No. PCT/EP98/03810 filed Jun. 22, 1998, the disclosures of which is expressly incorporated by reference herein.
The invention relates to a seat that can be tilted about its longitudinal center axis for generating a tilting movement of the pelvis of a sitting person. As used herein, the term xe2x80x9cseatxe2x80x9d includes all types of seat elements having a seat cushion and optionally a backrest, such as office chairs, bicycle seats, seats in motor vehicles, etc.
German Patent Document DE 195 47 964.5 discloses a seat in which the seat cushion can be tilted about its longitudinal or transverse axis. As a result of these tilting movements with limited small tilting angles, the pelvis of a sitting person, and thus the lumbar movement segments of the spinal column, are moved. In this manner, the intervertebral disks can sufficiently absorb nutrients, even during the otherwise static sitting operation, so that complaints involving the back caused be extended sitting are minimized. For better nourishing the intervertebral disks, particularly a lateral tilting movement of the pelvis is particularly suitable.
German Patent Document DE 33 24 788 A1 discloses an office chair whose seat cushion can be moved up and down and back and forth by means of adjusting elements.
It is an object of the invention to provide a method for generating the described tilting movement of a seat, particularly a vehicle seat.
This and other objects and advantages are achieved by the seat arrangement according to the invention, in which at least one pair of adjusting elements are arranged in mutually opposite areas of the seat cushion and can be controlled to carry out a lifting movement in opposite directions between a lower and an upper position. As the result of the diametrically opposed upward and downward movement, a tilting movement is achieved about a longitudinal or transverse axis of the seat. Care should be taken in this case that the tilting axis is situated as close as possible to the ischial tuberosities of the person sitting on the seat cushion. Also, the adjusting elements must generate only a pure tilting movement; an upward and downward movement of the sitting person, which would result in a sustained impairment of his well-being, must absolutely be avoided.
It is of course apparent that more than only one adjusting element can be provided in each lateral or forward and rearward half of the seat cushion. The adjusting elements, which are assigned to one another in pairs, are preferably controlled reciprocally by way of a common drive. It is also possible to control each adjusting element individually.
According to one embodiment of the invention, the whole seat surface is tilted, which can be implemented particularly in the case of seat constructions with a rigid seat bucket.
Also, the adjusting elements may be arranged between the supporting structure and the cushion part. The supporting structure itself may have a spring-equipped construction.
When the adjusting elements are arranged directly in the cushion, only slight changes are required on the supporting structure of the seat. Because of the narrow distance of the adjusting elements from the ischial tuberosities of the sitting person, a direct transmission of the tilting movement takes place. The adjusting elements may also be arranged in a direct line below the ischial tuberosities. As the result of the cushion layer situated in-between, the movement of the adjusting elements is slightly cushioned and, for increasing the sitting comfort, the tilting movement may be slightly weakened. Care should generally be taken when inserting the adjusting elements that the sitting comfort is impaired as little as possible by the adjusting elements inserted close to the body.
Adjusting elements according to another feature of the invention have a particularly simple construction and can be adapted particularly easily to the respective application. Furthermore, they can be produced at reasonable cost. Elements with flexible walls can, for example, be used as adjusting elements, such as bubbles or bellows made of a rubber-elastic material. Because of the relatively high stresses exerted by the weight of a sitting person, it is recommended that the bubbles, bellows, etc. be reinforced with a fabric insert. Rolling bellows are particularly suitable because they have plane-surface stiff boundaries on the top and bottom side for a linking to the seat structure. With the same effect as the above-mentioned adjusting elements, short-stroke cylinders with a rigid chamber wall can also be used. Such cylinders are distinguished by a correspondingly large diameter while the adjusting path is short and therefore require an installation space which corresponds essentially to the space requirement of bellows-type adjusting elements.
The adjusting elements referred to above may be operated by means of air or a liquid. Air-filled adjusting elements are particularly suitable for the arrangement in the cushion part of the seat cushion, because they adapt to the shape of the ischial tuberosities and do not provide the impression of a hard insert. However, because of the pressure dependence and temperature dependence of the air volume in the adjusting elements, suitable measures are required for controlling the adjusting path of the adjusting elements, for example, by means of a path measurement at the adjusting elements.
If the adjusting elements are operated by a liquid medium, because of the incompressibility of the liquid, a defined and reproducible adjusting path can be implemented, so that the control or automatic control of the adjusting path can take place by way of a simple measuring of the volume flow to and from the adjusting element. However, because of the inflexibility of liquid-filled adjusting elements, an arrangement directly in the cushion close to the ischial tuberosities of a sitting person is possible only with limitations.
The medium for the adjusting elements may be provided in separate working chambers. In this case, when the medium from the first working chamber is transferred into the pertaining adjusting element, it is simultaneously withdrawn from the other adjusting element into the second working chamber, so that the antiphase movement according to the invention is automatically adjusted. Evacuation of the adjusting element situated in its raised position is promoted by the weight of the sitting person. The working chambers as well as the drive for the volume displacement may advantageously be arranged outside the immediate sitting area, so that only a small space is required within the seat or the seat cushion.
According to another feature of the invention, the tilting movement can be implemented, for example, by a double-acting pneumatic or hydraulic cylinder. In the case of a liquid working medium, a defined and reproducible working stroke of the adjusting elements can be achieved by measuring the piston path. Instead of the working chambers formed in the cylinder, bellows-shaped working chambers may also be provided.
Another embodiment of the invention has no separate working chambers for the medium. As a result, a particularly simple construction is achieved, while the installation space is very small. The medium is pumped back and forth directly between the two adjusting elements, without any separate reservoir from which the medium is taken or into which the medium is returned. Thus, a xe2x80x9cclosed pendulum systemxe2x80x9d is obtained with a particularly low filling amount of medium.
Generally all known embodiments of pumps can be used as pressure medium pumps. When a sliding vane rotary pump is used, it is an advantage in conjunction with a liquid medium that, per revolution of the pump, a measurable and largely constant volume is delivered. By detecting the rotational speed of the pump, the adjusting elements can be controlled or automatically controlled in a simple manner. The entering of a constant center position of the adjusting elements is also easily possible. By the corresponding automatic control of the rotational speed of the pump, the course of the adjusting movement can be controlled over time.
In principle, instead of a sliding vane rotary pump, a piston pump can be used which, when a liquid medium is used, also delivers a measurable volume flow. Because of the occurring pulsations, the use of piston pumps is limited to smaller individual volumes. Optionally, multipiston pumps can be used.
In a further embodiment of the invention at least two adjusting elements are arranged above one another on two opposite areas of the seat cushion, each being able to carry out a defined adjusting path between the two defined and reproducible conditions xe2x80x9cadjusting element completely evacuatedxe2x80x9d and xe2x80x9cadjusting element completely filledxe2x80x9d. By the corresponding filling or evacuating of the individual adjusting elements, adjusting heights can be entered which differ in steps. According to the invention, this is possible without any path measurement, which would require a sensor system, with particularly low expenditures, for example, by means of a simple control by way of valves which generate only the two conditions xe2x80x9cpressurelessxe2x80x9d and xe2x80x9cfull operating pressurexe2x80x9d. The number of adjusting elements arranged above one another determines the number of the possible adjusting positions.
Elements with flexible walls, such as bubbles or bellows made of a rubber-elastic material, are preferably used as adjusting elements. Because of the relatively large stresses exerted by the weight of a sitting person, it is recommended that the bubbles, bellows, etc. be reinforced with a fabric insert. When bubble-type adjusting elements are used, a very low space requirement is obtained because the constructional height of the adjusting elements in the starting condition is determined only by the sum of their wall thicknesses. In a special manner, rolling bellows are also suitable because they have plane-surface stiff boundaries on the top and bottom side for the linking to the seat structure. With the same effect as the above-mentioned adjusting elements, short-stroke cylinders with a rigid chamber wall can also be used. Such cylinders are distinguished by a correspondingly large diameter while the adjusting path is short and therefore require an installation space which corresponds essentially to the space requirement of bellows-type adjusting elements.
In the case of two adjusting elements arranged above one another, three defined adjusting heights are obtained: The pressureless condition of both adjusting elements marks the lower position whose height, for example, in the case of bubble-type adjusting elements, is determined only by the sum of the wall thicknesses of the two bubbles. A center position is obtained by the admission of pressure to one of the two adjusting elements, while the second adjusting element remains pressureless. Finally the upper position can be entered in a defined manner by the admission of pressure to both adjusting elements. If the two adjusting elements have the same construction, a center position can be entered which is situated precisely in the geometrical center between the lower and the upper position. As the result of an alternating control in the opposite direction of the adjusting elements arranged in pairs in the two seat cushion areas, a tilting of the pelvis is achieved about the longitudinal or transverse axis of the seat. Naturally, the invention includes embodiments with more than two adjusting elements arranged above one another.
In the case of liquid-filled adjusting elements, the adjusting path (assuming a corresponding design of the adjusting element) is largely independent of the stressing of the adjusting element and of the ambient temperature. Thus, reproducible adjusting paths can be achieved in a particularly simple manner.
In contrast, pneumatic adjusting elements, as a rule, have a simpler construction and are easier to control than liquid-filled adjusting elements. Because of the compressibility of the gaseous medium and its considerable temperature dependence, the (maximal) adjusting path cannot be reproduced however. It is therefore suggested to automatically limit the adjusting path of the adjusting element by an additional device on the adjusting element. Thus, irrespective of the stressing of the pneumatic adjusting element, one defined maximal adjusting path respectively is maintained if the adjusting element is acted upon by an internal pressure which is higher than would be necessary because of the effective inner surface of the adjusting element and the respective loading by a sitting person. This ensures that a constant adjusting path is maintained without any additional measures, such as a path measurement.
According to another feature of the invention, path limitations are provided in the interior of the adjusting element. These path limitations consist preferably of a flexible, non-ductile material. In the case of adjusting elements with walls made of a plastic material, they can be welded directly to the adjusting element during the manufacturing. This results in a particularly simple construction and in a low-cost manufacturing.
As an alternativexe2x80x94viewed in the adjusting directionxe2x80x94opposite wall sections, in the case of adjusting elements made of a plastic material, can be welded in sections to one another so that, as the result of these welded connections, a path limitation is also achieved (comparable with quilting, for example, in the case of air mattresses). In addition, exterior path limitations are naturally also possible, in which case the partial or surroundingly ring-shaped looping around the adjusting element takes place, for example, by straps made of a flexible and non-ductile material. Preferably, the path limitation on the outer circumference of the adjusting element is additionally fixed in order to reliably prevent a sliding-off in the pressureless condition of the adjusting element.
When a gaseous pressure medium is used to operate the adjusting elements, it is essential that a sufficiently high pressure be available in order to be able to reliably maintain respective constant adjusting paths (and therefore defined limited tilting angles) in conjunction with the path limitation according to the invention independently of the stressing by the sitting person. The adjusting elements can be controlled by way of simply constructed valves, without need for a sensor system for evaluating the respective existing adjusting height. In addition, in the case of several seats (for example, in a vehicle), a central air feed with a single pressure source is sufficient.
In a further embodiment of the invention, a shut-off valve can be provided between the adjusting elements (for example, the two seat halves) to prevent reliably an exchange of the medium between the adjusting elements. The shut-off valve is activated by the user when the device for generating a tilting movement is switched off and the seat cushion is to be fixed in a xe2x80x9cslantedxe2x80x9d position (the adjusting elements are xe2x80x9clockedxe2x80x9d at different heights). The shut-off valve prevents a slow flowing-over of the medium, for example, as the result of leakage losses in a pump. Such an application can be considered, for example, for seat users who require a slanted position of the seat cushion for orthopaedic reasons.
The tiltable seat according to the invention can be operated by means of a motor-operated adjusting drive, for example, an electric motor or by means of a pressure medium. Electric motors, in particular, are distinguished by a low space requirement and a simple controllability. The motor-operated adjusting drives may be combined with all known transmission elements, such as rotatory or linear transmissions, eccentrics, toothed racks, etc. In the case of the pressure medium drive, hydraulic media are preferred because of the better automatic control possibilities and the higher working pressures.
In most cases, direct implementation of the adjusting movement by way of lever arms requires a transmission for the power ratio; rotatory as well as linear transmissions are conceivable, depending on the manner of generating the power.
In another embodiment of the invention, spindle drives are driven by a rotary motor and convert its rotating movement into a vertical movement. Preferably, a common drive shaft is to be provided for the adjusting elements arranged in pairs. This also applies to eccentric drives and lifting linkages.
Height changes in the region of the ischial tuberosities of the sitting person can be achieved by means of wedge-shaped elements, particularly wedge-shaped disks, which are rotated relative to one another. In this case, the wedge-shaped disks can be disposed with respect to one another by way of rolling bodies for reducing friction.
In still another embodiment, the seat cushion is tilted by an adjusting element applied to one side. Such tilting is particularly appropriate in those seats whose seat cushion has a rigid xe2x80x9cseat bucketxe2x80x9d which can be tilted as a whole about a defined center axis. Tilting by way of an adjusting element applied to one side can also be used, however, in seats with a spring core substructure, in which case, tilting takes place about an axis approximately in the center of the seat cushion, automatically. The adjusting element is preferably arranged outside the supporting structure of the seat cushion. An arrangement of the adjusting element between the supporting structure and the cushion part is also conceivable. All above-indicated embodiments can, for example, be used as adjusting elements.
As mentioned above, when the adjusting elements are actuated by a liquid medium, advantages occur with respect to the control or automatic control of the adjusting path, because, by way of measuring the volume flow, a defined adjusting path can be achieved.
According to yet another embodiment of the invention, a constant center position can be achieved, irrespective of the sitting position or the body weight of the seat user, by means of a bubble-type adjusting element.
Certain pump configurations (for example, sliding vane rotary pumps) emit a fixed number of measurable pulses with each revolution, with a linear relationship between the number of pulses and the delivered amount of liquid. However, within defined limits, the delivered liquid flow is a function of various parameters, such as the driving direction of the pump, pumping or suction operation, the pressure level against which the delivery or the suction takes place, etc.
In the process according to the invention, in a closed system, in which the pump conveys a defined liquid volume back and forth between two adjusting elements 1 and 2, a starting condition is first defined in which one of the adjusting elements (such as the adjusting element 1) is just completely evacuated. This condition can be clearly determined by means of a steep pressure drop in the pump which occurs when the adjusting element is evacuated. Hereinafter the latter condition will be called the initial value L12, (wherein L=xe2x80x9cadjusting element emptyxe2x80x9d, and 12=xe2x80x9cpumping direction from adjusting element 1 into adjusting element 2xe2x80x9d). Subsequently, the pump delivers the liquid back into the previously evacuated adjusting element 2, until a fictitious center position of the adjusting element 2 (and thus also of the adjusting element 1) has been reached. In this case, the pump is controlled by means of a pulse number which is based on a preset value, so that, for the first cycle after the start of the operation of the system, under certain circumstances, first an incorrect (xe2x80x9cslantedxe2x80x9d) center position may still be generated. Then, the adjusting element 2 is completely filled. The measurement for complete filling will be the pressure drop in the now completely evacuated adjusting element 1 (final value V12, wherein V=xe2x80x9cadjusting element fullxe2x80x9d). The number of pulses N12 between the values L12 and V12 delivered by the pump is filed in a data memory.
In the same manner, the final value V21 is determined for the reverse pumping direction from the adjusting element 2 into the adjusting element 1. The starting point for such counting is the initial value L21 (corresponding to the value V12). Thus, a pulse number N21 is obtained for the second pumping direction.
After the first complete cycle, with N12 and N21, measuring numbers are now available which indicate how many pulses are required in each case for the complete pumping over of the liquid between the two adjusting elements. The measuring numbers N12 and N21 are multiplied by previously empirically determined factors F12 and F21, which are constant for a particular construction of a unit consisting of the seat and the adjusting elements. Since, as a rule, the factors F12 and F21 deviate only slightly from one another, in a simplified technique, a uniform factor F can also be used for the two pumping directions.
By means of the product F12xc2x7N12 or F2xc2x7N21, in the subsequent cycle, the exact geometrical center position of the two adjusting elements is entered. In this case, it is significant that such center positioning can be achieved without any direct path measurement, so that the process according to the invention is distinguished by very low expenditures. By means of the measuring numbers N12 and N21, the respective loading of the seat by the occupant is taken into account, so that, already after a single initialization cycle (in which the values N12 and N21 are determined), the geometrical center position of the adjusting elements is precisely maintained.
The loading of the seat is significantly influenced by the seat user""s body weight and the contact surface between the seat user and the seat cushion. In addition, the sitting position of the seat user also influences the values N12 and N21, depending on whether the right and the left or the forward and the rearward seat half is loaded more. Thus, according to the process of the invention, the systems adapts itself not only to different seat users but also dynamically to changing sitting positions of one and the same seat user.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.